Define requirements for templates

[bannert1337]

The app templates often do not follow a basic structure.
Therefore, a basic structure should be defined that templates must fulfil to be included.

Potential requirements:

• Templates should be deployable without configuration (configuration should be optional)
• Templates should follow a guideline to handle Docker volumes and paths (use Docker volumes by name or map paths to the container)
• Templates should be automatically testable by CI/CD
• Templates should only be added if they pass CI/CD tests
• Templates should be unique (no multiple entries for the same service)
• Templates should have a unique logo
• (additional requirements)

Please mention requirements in this issue.